Add border to stick btn and input

See https://github.com/marienfressinaud/FreshRSS/issues/563

p/themes/Flat/flat.css

@@ -49,6 +49,7 @@ input, select, textarea {
 	background: #fff;
 	border: none;
 	border-bottom: 3px solid #ddd;
+	border-left-color: #ddd;
 	color: #666;
 	border-radius: 5px;
 }
@@ -155,10 +156,17 @@ form th {
 .stick .btn + .dropdown > .btn {
 	border-radius: 0 5px 5px 0;
 }
+.stick .btn + .btn,
 .stick .btn + input,
+.stick .btn + .dropdown > .btn,
+.stick input + .btn,
 .stick input + input,
-.stick .dropdown + input {
-	border-left: 1px solid #ddd;
+.stick input + .dropdown > .btn,
+.stick .dropdown + .btn,
+.stick .dropdown + input,
+.stick .dropdown + .dropdown > .btn {
+	border-left-width: 1px;
+	border-left-style: solid;
 }
 
 .btn {
@@ -175,6 +183,7 @@ form th {
 	border-radius: 5px;
 	border: none;
 	border-bottom: 3px solid #2980b9;
+	border-left-color: #2980b9;
 	color: #fff;
 }
 a.btn {
@@ -196,6 +205,7 @@ a.btn {
 	background: #e67e22;
 	color: #fff;
 	border-bottom: 3px solid #d35400;
+	border-left-color: #d35400;
 }
 .btn-important:hover,
 .btn-important:active {
@@ -206,6 +216,7 @@ a.btn {
 	background: #e74c3c;
 	color: #fff;
 	border-bottom: 3px solid #c0392b;
+	border-left-color: #c0392b;
 }
 .btn-attention:hover,
 .btn-attention:active {