How to Show Only Corner Borders

div {    position: relative;    width: 100px;    height: 100px;    margin: 20px;    border: 1px solid #000;}
div:after {    display: block;    content: "";    width: 20px;    height: 20px;    position: absolute;    top: -5px;    right: -5px;    border-top: 3px solid blue;    border-right: 3px solid blue;}span:before {    display: block;    content: "";    width: 20px;    height: 20px;    position: absolute;    bottom: -5px;    left: -5px;    border-bottom: 3px solid orange;    border-left: 3px solid orange;}

<div><span></span></div>

Border at corner only in flutter

This can be done with CustomPaint widget with CustomPainter set as foregroundPainter:

    import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'CustomPaint spotlight',
      home: Scaffold(
        appBar: AppBar(
          title: Text('CustomPaint spotlight'),
        ),
        body: Center(
          child: CustomPaint(
            foregroundPainter: BorderPainter(),
            child: Container(
              width: 200,
              height: 100,
              color: Colors.deepOrange[50],
            ),
          ),
        ),
      ),
    );
  }
}

class BorderPainter extends CustomPainter {
  @override
  void paint(Canvas canvas, Size size) {
    double sh = size.height; // for convenient shortage
    double sw = size.width; // for convenient shortage
    double cornerSide = sh * 0.1; // desirable value for corners side

    Paint paint = Paint()
      ..color = Colors.black
      ..strokeWidth = 1.5
      ..style = PaintingStyle.stroke
      ..strokeCap = StrokeCap.round;

    Path path = Path()
      ..moveTo(cornerSide, 0)
      ..quadraticBezierTo(0, 0, 0, cornerSide)
      ..moveTo(0, sh - cornerSide)
      ..quadraticBezierTo(0, sh, cornerSide, sh)
      ..moveTo(sw - cornerSide, sh)
      ..quadraticBezierTo(sw, sh, sw, sh - cornerSide)
      ..moveTo(sw, cornerSide)
      ..quadraticBezierTo(sw, 0, sw - cornerSide, 0);

    canvas.drawPath(path, paint);
  }

  @override
  bool shouldRepaint(BorderPainter oldDelegate) => false;

  @override
  bool shouldRebuildSemantics(BorderPainter oldDelegate) => false;
}

This produces the result like:

You need to know that CustomPaint does not crop its child corners and in some cases that might be discouraging. You have two ways of solving this:

• Easy one - to cast rounded borders on its child and make them be visibly equal to CustomPaint borders.

• Robust one - to wrap child with ClipPath with a path that copies CustomPaint path

    import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'CustomPaint spotlight',
      home: Scaffold(
        appBar: AppBar(
          title: Text('CustomPaint spotlight'),
        ),
        body: Center(
          child: CustomPaint(
            foregroundPainter: BorderPainter(),
            child: ClipPath(
              clipper: BorderClipper(),
              child: Container(
                width: 200,
                height: 100,
                color: Colors.deepOrange[50],
              ),
            ),
          ),
        ),
      ),
    );
  }
}

class BorderPainter extends CustomPainter {
  @override
  void paint(Canvas canvas, Size size) {
    double sh = size.height; // for convenient shortage
    double sw = size.width; // for convenient shortage
    double cornerSide = sh * 0.1; // desirable value for corners side

    Paint paint = Paint()
      ..color = Colors.black
      ..strokeWidth = 1.5
      ..style = PaintingStyle.stroke
      ..strokeCap = StrokeCap.round;

    Path path = Path()
      ..moveTo(cornerSide, 0)
      ..quadraticBezierTo(0, 0, 0, cornerSide)
      ..moveTo(0, sh - cornerSide)
      ..quadraticBezierTo(0, sh, cornerSide, sh)
      ..moveTo(sw - cornerSide, sh)
      ..quadraticBezierTo(sw, sh, sw, sh - cornerSide)
      ..moveTo(sw, cornerSide)
      ..quadraticBezierTo(sw, 0, sw - cornerSide, 0);

    canvas.drawPath(path, paint);
  }

  @override
  bool shouldRepaint(BorderPainter oldDelegate) => false;

  @override
  bool shouldRebuildSemantics(BorderPainter oldDelegate) => false;
}

class BorderClipper extends CustomClipper<Path> {
  @override
  Path getClip(Size size) {
    double sh = size.height; // for convenient shortage
    double sw = size.width; // for convenient shortage
    double cornerSide = sh * 0.1;

    Path path = Path()
      ..moveTo(cornerSide, 0)
      ..quadraticBezierTo(0, 0, 0, cornerSide)
      ..moveTo(0, sh - cornerSide)
      ..quadraticBezierTo(0, sh, cornerSide, sh)
      ..moveTo(sw - cornerSide, sh)
      ..quadraticBezierTo(sw, sh, sw, sh - cornerSide)
      ..moveTo(sw, cornerSide)
      ..quadraticBezierTo(sw, 0, sw - cornerSide, 0);
    return path;
  }

  @override
  bool shouldReclip(CustomClipper<Path> oldClipper) => false;
}

How to create CSS border corners around text

h1 {  display: inline-block;  position: relative;  padding: 10px;}
h1:before,h1:after {  height: 14px;  width: 14px;  position: absolute;  content: '';}
h1:before {  right: 0;  top: 0;  border-right: 3px solid #9b59b6;  border-top: 3px solid #9b59b6;}
h1:after {  left: 0;  bottom: 0;  border-left: 3px solid black;  border-bottom: 3px solid black;}

<h1>TEXT</h1>

.special_button{    position: relative;    background-color: white;    height: 60px;    line-height:60px;    font-size: 32px;    font-family: dosis_light;    border:none;    padding:0 15px;}
.special_button::before,.special_button::after{    position: absolute;    content: '';    width: 33px;    height: 20px;}
.special_button::before{    left:0;    top:0;    border-left:3px solid black;    border-top:3px solid black;}.special_button::after{    right:0;    bottom:0;    border-right:3px solid black;    border-bottom:3px solid black;}

<button class="special_button">ME CONTACTER</button>

//
//  CornerView.swift
//  CornersViewSO
//
//  Created by Reinier Melian on 5/31/17.
//  Copyright © 2017 Reinier Melian. All rights reserved.
//

import UIKit
import CoreGraphics

@IBDesignable
class CornerView: UIView {

    @IBInspectable
    var sizeMultiplier : CGFloat = 0.2{
        didSet{
            self.draw(self.bounds)
        }
    }

    @IBInspectable
    var lineWidth : CGFloat = 2{
        didSet{
            self.draw(self.bounds)
        }
    }

    @IBInspectable
    var lineColor : UIColor = UIColor.black{
        didSet{
            self.draw(self.bounds)
        }
    }


    override init(frame: CGRect) {
        super.init(frame: frame)
        self.backgroundColor = UIColor.clear
    }

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        self.backgroundColor = UIColor.clear
    }

    func drawCorners()
    {
        let currentContext = UIGraphicsGetCurrentContext()

        currentContext?.setLineWidth(lineWidth)
        currentContext?.setStrokeColor(lineColor.cgColor)

        //first part of top left corner
        currentContext?.beginPath()
        currentContext?.move(to: CGPoint(x: 0, y: 0))
        currentContext?.addLine(to: CGPoint(x: self.bounds.size.width*sizeMultiplier, y: 0))
        currentContext?.strokePath()

        //top rigth corner
        currentContext?.beginPath()
        currentContext?.move(to: CGPoint(x: self.bounds.size.width - self.bounds.size.width*sizeMultiplier, y: 0))
        currentContext?.addLine(to: CGPoint(x: self.bounds.size.width, y: 0))
        currentContext?.addLine(to: CGPoint(x: self.bounds.size.width, y: self.bounds.size.height*sizeMultiplier))
        currentContext?.strokePath()

        //bottom rigth corner
        currentContext?.beginPath()
        currentContext?.move(to: CGPoint(x: self.bounds.size.width, y: self.bounds.size.height - self.bounds.size.height*sizeMultiplier))
        currentContext?.addLine(to: CGPoint(x: self.bounds.size.width, y: self.bounds.size.height))
        currentContext?.addLine(to: CGPoint(x: self.bounds.size.width - self.bounds.size.width*sizeMultiplier, y: self.bounds.size.height))
        currentContext?.strokePath()

        //bottom left corner
        currentContext?.beginPath()
        currentContext?.move(to: CGPoint(x: self.bounds.size.width*sizeMultiplier, y: self.bounds.size.height))
        currentContext?.addLine(to: CGPoint(x: 0, y: self.bounds.size.height))
        currentContext?.addLine(to: CGPoint(x: 0, y: self.bounds.size.height - self.bounds.size.height*sizeMultiplier))
        currentContext?.strokePath()

        //second part of top left corner
        currentContext?.beginPath()
        currentContext?.move(to: CGPoint(x: 0, y: self.bounds.size.height*sizeMultiplier))
        currentContext?.addLine(to: CGPoint(x: 0, y: 0))
        currentContext?.strokePath()
    }


    // Only override draw() if you perform custom drawing.
    // An empty implementation adversely affects performance during animation.
    override func draw(_ rect: CGRect) {
        // Drawing code
        super.draw(rect)
        self.drawCorners()
    }


}

import UIKit

class ViewController: UIViewController {

    var cornerViewCode : CornerView?
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.

        self.cornerViewCode = CornerView(frame: CGRect(x: 0, y: 0, width: 50, height: 50))
        self.view.addSubview(self.cornerViewCode!)
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }


}